Wind turbines are provided with a rotor shaft which is part of an electrical generator producing electricity during a movement of the rotor relative to the stator of the generator. The stator comprises a number of coils or windings; the rotor comprises a number of permanent magnets so that an electric voltage is induced when the rotor is turned.
During rotation of the rotor a certain amount of heat is generated in the stator. For conventional wind turbines different cooling means are known. It has been proposed to use an air cooled ventilation system, a water cooled system, as well as heat pipes. In a water cooled system cooling pipes are employed between the windings of the stator in order to remove the generator teeth from the stator. However, such conventional water cooling systems are complicated and costly from the manufacturing and serviceability point of view, due to the difficulty of separating cooling pipes and the windings of the stator coils from one another. Furthermore the output torque of the generator is reduced due to the fact that the fill factor is reduced due to the cooling pipes. Alternatively the flux density in the stator yoke is reduced due to saturation.